This research investigates interseismic deformation in the Pacific Northwest, focusing on the Cascadia megathrust. Utilizing the viscoelastic earthquake-cycle model, the study incorporates the Cascadia megathrust into deformation models spanning the Western U.S. The research generates new estimates of slip deficit rates along the Cascadia margin, emphasizing the need for glacial-isostatic adjustment corrections and examining the influence of assumed ductile properties on the results.
Interseismic deformation in the Pacific Northwest is constrained by the horizontal crustal velocity field derived from the Global Positioning System (GPS) in addition to vertical rates derived from GPS, leveling, and tide gauge measurements. Such measurements were folded into deformation models of fault slip rates as part of the 2023 National Seismic Hazard Model (NSHM) update. This study builds upon one of the contributing models, the viscoelastic earthquake-cycle model of Pollitz.
This model permits inclusion of effects of time-dependent viscoelastic relaxation within earthquake cycles (i.e., 'ghost transients') and laterally variable elastic and/or ductile material properties. The study leverages these capabilities to incorporate the Cascadia megathrust into Western U.S.-wide deformation models in which crustal fault slip rates are estimated simultaneously with slip deficit rates along the interplate boundary between the descending Juan de Fuca plate and the North American plate. This effort includes construction of a margin-wide model of viscoelastic structure founded on the Slab 2.0 model and probes different models of the ductile properties of the surrounding oceanic asthenosphere, continental lower crust, and mantle asthenosphere. This results in new estimates of the distribution of slip deficit rate along the ∼ 1000 km long margin, highlights the importance of correcting for glacial-isostatic adjustment effects, and permits assessment of sensitivity of results to assumed ductile properties.
Cascadia Megathrust Interseismic Deformation Viscoelastic Models Slip Deficit Rates Glacial-Isostatic Adjustment
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